Single seed-syllables — Aiṃ, Hrīṃ, Śrīṃ, Klīṃ, Krīṃ, and others — each held to condense a deity's power into one sound.
Canonical definition
A bīja ("seed") mantra is a single Sanskrit syllable, usually ending in the nasal sound anusvāra (ṃ), believed in Tantric and Āgamic traditions to be the sonic essence or "seed form" of a particular deity or cosmic principle. Unlike Vedic mantras, bīja mantras generally have no literal semantic meaning as words — their power is understood to lie in the sound itself. This category is especially prone to uncredentialed claims online; every card here will name a specific textual source (such as the Mantra Yoga Saṃhitā or a named Tantra) for any deity association given.